Metallic apparatus for carrying out chemical and other processes



Patented see. 2,- 1930 CIULNITEDCF-STARTES PATENT OFFICE FRANZ LAPPE AND ianwm KOCH, or LUDWIGSHAEEN-ON-THE-RHINE, MATHIAS mm F HEIIDELBERG, AND/HANS SAUER, 0F NEUROSSEN, GERMANYQASSIGNORS TO I. G. I, FARBENLNDUSTRIE AKTIENGESELLSCHAFT, or FRANKFORT-ON-THE-MAIN, GER- MANY, A CORPORATION OF GERMANY METALLIC APPARATUS FOR CARRYING OUT CHEMICAL D OTHER PROCESSES No Drawing. Application filed March 23, 1927, Serial No: 177,8;30, and in Germany March 25, 1926:

l/Vhen' carrying out chemical and other processes with gases, vapors, liquids and the like, which contain hydrogen, oxygen or sulfur, or several of these elements (for the purpose of the present invention these elements a may be referred to as destroying elements) in a .free or combined state, in metallic apparatus, as for example such as are made of steel or copper, andespecially when pressures or high temperatures are employed, a loosening of. the structure of the metal, tending to porosity and fracture of the material, occurs after a short period of exposure to such high temperatures or pressures. Consequently the affected parts of the apparatus very soon become unfit for use.

We have now found that ,these drawbacks may be overcome by constructing the apparatus of metals or alloys which are particularly free fromdmpurities, such as oxygen, sulfur, carbon and the like, .Such materials may be prepared either by direct metallurgical working, or by treating metals of an ordinary type at high temperatures with gases which react with the'impurities in the metals or alloys to form volatile compounds, so that the said impurities are eliminated. Hydrogen, or mixtures of reducing and oxidizing gases such'as gas mixtures containing hydrogen, water vapor, carbon monoxidor cai'bon dioxid, with or ,withoul; an admixture of inert gases may be mentioned as examples of gases suitable for this purpose. When mixed gasesare used, the relative proportions of will result.

For example, iron prepared with the aid of manganese by the Martin smelting process, and which is freed from oxid as completely as possible, forms a very suitablematerlal for the apparatus; or a tube or other article made a i of ordinary mild steel (ingot steel) may be the oxidizing and reducing gases should be adjusted so that, no oxidation of the metaldrawbacks above referred to and'the appara- V tus or parts of apparatus constructed of them have an-exceedingly long working life.

For example, whenaqueous solutions, such as those of sodium hydroxid, sodium nitrate, ammonium nitrate and the like are concentrated in vessels made of wrought iron or the like, extensive destruction of the vessels occurs after a comparatively short time, wherc- O as when vessels constructed of iron which has C0 to a large extent been freed from impurities, as for example in the manner described, are used, the apparatus may be kept in use for a long time without revealing any substantial corrosion of the material. Again, when working with nitrous gases (i. e. gases containing nitrogen oxids), for example'in cast iron or wrought iron apparatus there is soon noticeable an extensive destruction in the shape of cracking or peeling of the material which,

however, does not occur when the iron used apparatus quickly sufifers extensive injury,

which does not occur when the apparatus is constructed of metals or alloys treated in the manner herein described. We have also found that there is not always a need to treat the metalfor such a length of'time that all the impurities are eliminated. Inmany cases the treatment may be interrupted at an earlier stage, since it frequently happens that the impurities become harmless after a less protracted treatment.

In order to determine whethenthe metals or alloys are suitable for the particular purpose required, a sample of the material to be used may be treated athigh temperatures, and under pressure if necessary, with gases, vapors or liquids which contain'free or com- 95 bined oxygen or sulfur and which are hereinafter referred to as corroding agents and preferably in the presence of hydrogen. The microscopic examination of the treated sample willreveal whether the material is 100 suitable, because if it is not, the sample will exhibit the effects of corrosion in the bound-. aries of the grains. It is often advisable, prior to making such microscopic examination, to subject the treated sampleto a superficial oxidation, such as is usual in the case of iron by annealing till blue, since under these conditions the interstitial substance between the grains is more clearly visible. The temperatures to be employed for this purpose will depend on the nature of the metals or alloys under examination. When ascertaining the suitability of iron, steel and the like, higher temperatures will naturally be used than when examining such metals as aluminium or magnesium. The temperatures to be employed in these tests are substantially higher generally speaking than the Working temperatures of the apparatus made of the metals or alloys under examination. When the working is. to'be carried out under pressure in the apparatus, it is also advisable to carry out the tests under pressure. Commercial iron, construction steel for example, becomes corroded by the formation of inclusions at the boundaries of the grains when the working operations are carried on with gases containing hydrogen, in the presence of oxygen or sulfur,.free or combined, at raised temperature and under pressure, the iron thereby losing its mechanical strength, which result will in practice become apparent'only after it has been in use for, some months. If, however, a sample of such iron be treated with a weakly oxidizing mixture of hydrogen and water vapor for 144 hours under a pressure of about 150 atmospheres and at a temperature of 550 to 600 (3., the

or alloys which have been largely freed from microscopic examination will disclose corrosion round the grains of the metal, thereby quickly shewing that the iron under examination is unsuitable for the purpose required.

WVhcn a sample of commercial iron is treated with a gas at a high temperature, for example in the manner above described, the microscopic examination will not reveal any such corrosion, and the metal will prove very suit; able for the required purpose.

It may also be advantageous not only to construct the apparatus of the said metals impurities or in which the impurities have been rendered innocuous, but to apply to it further acoating of resistant material, this coating being applied at least to the parts which are most exposed to attack. Chroinium, tungsten, uranium, manganese, alu-. minium, silver, copper, enamel; and the like may be mentioned as highly resistant materials suitable for such coating. Apparatus of this kind display unusually high resistance and may be kept in use for a long time without shewing any corrosion.

What we claim is:

1. Metallic apparatus for carrying out processes in the presence of destroying elements whlch'comprise iron which has been treated at high temperatures-and under consaid metal, the said iron on being treated with corroding agents and then subjected to microscopic examination no longer showing the efiects of corrosion in the boundaries of the microscopic grains.

2. Metallic apparatus for carrying outprocesses in the presence of destroying elements which comprise iron which has been treated at high temperatures and under conditions precluding oxidation, with a gas capableofforming gaseous compounds with theimpurities originally contained -in the said metal, in such a manner that the impurities are" present after the treatment in an innocuous form, the said iron on being treated with corroding agents and then subjected to microscopic examination no longer showing the effects of corrosion in the boundaries of the microscopic grains.

3. Metallic apparatus for carrying out processes in the presence of destroying elements which comprise iron which has been treated at high temperatures with hydrogen, the said iron on being treated with corroding agents and then subjected to microscopic examination no longer showing the efi'ects of 'corrosion in the boundaries of the micro scopic grains.

In testimony whereofiwe have hereunto set our hands.

' FRANZ LAPPE.

EDWIN KOCH. MATHIAS PIER. HANS SAUER, 

